1. Field of the Invention
The present invention relates to color picture tubes, and more particularly, to a tension mask frame assembly for a color picture tube, which is installed adjacent to a fluorescent film in a panel and performs a color distinction function.
2. Description of the Related Art
In color picture tubes adopted in computer monitors and televisions, three electron beams emitted from an electron gun land on red, green and blue fluorescent materials on a fluorescent film, which is formed on the screen surface of a panel, through electron beam passing holes of a mask which has a color distinction function, and excite the fluorescent materials, where a picture is formed.
In the above-described color picture tubes for forming a picture, types of a mask having a color distinction function include a dot mask which is adopted in computer monitors and a slot mask (which is also called a slit mask) which is adopted in televisions. Since the screen surface of a panel is formed to have a predetermined curvature in consideration of the landing of deflected electron beams, dot masks and slot masks are designed to have a curvature corresponding to the curvature of the screen surface.
These masks are formed by etching a 0.1-0.25 mm (millimeters) thin plate, forming a plurality of electron beam pass holes and forming the thin plate in a predetermined curvature. If the mask has not a predetermined curvature or greater, the structural strength of the mask is weak. Thus, in many cases, this mask is permanently plastic-deformed during the manufacture of cathode-ray tubes or during the transportation of cathode-ray tubes. Consequently, this mask may not perform a color distinction function. However, a mask molded to have a predetermined curvature is supported by a frame and installed on the inner surface of a panel. The mask is easily heated and thermally expanded by thermal electrons emitted from an electron gun, and doming occurs, preventing color distinction of three electron beams.
Recent color picture tubes pursue flattening of a screen surface because the development of enlargement of color picture tubes causes distortion of a picture depending on the curvature of the screen surface and requires reproduction of natural pictures.
Slot masks for preventing the doming of a mask and flattening the screen surface of a panel have been disclosed in U.S. Pat. No. 3,638,063 for Grid Structure for Color Picture Tubes issued to Tachikawa et al., U.S. Pat. No. 4,942,332 for Tied Slit Mask for Color Cathode Ray Tubes issued to Adler et al., U.S. Pat. No. 4,926,089 for Tied Slit Foil Shadow Mask with False Ties issued to Moore and U.S. Pat. No. 4,973,283 for Method of Manufacturing a Tied Slit Mask CRT issued to Adler et al.
An aperture grille-type mask frame assembly includes strips spaced predetermined intervals apart from each other in parallel to form slots. Both ends of the strips are supported by a frame so that the mask has a tensile force. The strips are connected to each other by damper wires, in order to prevent the strips from vibrating independently.
However, the mask frame assembly is not easy to handle during the manufacture because of its structure in which the strips formed on a plate are parallel to each other and secured at only both ends thereof.
In order to solve this problem, a slot mask disclosed in U.S. Pat. No. 4,942,332 issued to Tachikawa et al. has a structure in which a plurality of strips are spaced predetermined intervals apart from each other on a thin plate to form slits and connected to adjacent strips by tie bars.
Since the strips of this mask are connected to each other by tie bars, howling vibration generated by external impacts and acoustic waves can be more or less reduced. But, the vibration of tie bars is transmitted between adjacent strips, so that the reduction of the howling is not large.
To solve this problem, a color cathode-ray tube is disclosed in Japanese Patent Publication No. 2000-77007 for Color Cathode-ray Tube by Watanabe. In this color cathode-ray tube there is a shadow mask on which a plurality of slots are formed is installed on a frame so that a tensile force is applied to the shadow mask. The frame includes a vibration damper which contacts the edge of the shadow mask.
The cathode-ray tube having such a structure dampens vibration by adhering the vibration damper to the shadow mask. However, the shadow mask is a thin plate through which slots are formed, and transmits vibration well via media for transmitting vibration, that is, via real bridges for defining slots, so that a sufficient amount of vibration cannot be dampened by the vibration damper 33 alone.
Another shadow mask frame assembly includes a frame, a mask and an earing. The mask is tensed and secured to the frame, and has strips spaced predetermined intervals apart from each other in parallel and a plurality of real bridges which connect the strips to each other to define the slots. The earing is hung through the end strip of the mask in order to dampen the vibration of the mask.
This mask frame assembly intends to extinguish a vibration applied to the mask using the friction of the end strip and the earing. However, the friction of the end strip and the earing creates noise. Also, the strips on the mask are connected to each other by a plurality of real bridges, so that vibrations are transmitted well via the bridges. Thus, although a vibration generated on the center portion of the mask is dampened by the earrings after being transmitted to the end strip, a sufficient vibration damping effect cannot be expected.
In this mask, scanning electron beams interfere with holes arranged on a mask, which causes a moire phenomenon. Since the spots of electron beams which land on a fluorescent film are deformed into horizontally-long spots by the strong pin cushion magnetic field of a deflection yoke as the deflection angle of electron beams increases, severe moire phenomenon occurs at the peripheral portion of a screen. Thus, selection of a mask pitch that minimizes the moire phenomenon and reduction of the vertical pitch of a mask to reduce the depth of modulation have been used.
These methods, by which the transmissivity of the peripheral portion of a mask is reduced, are not desirable in terms of the uniformity of the luminance of a screen.
Also, in the case of these masks, a mask domes severely by the heat from electron beams. Furthermore, the doming is prone to occur at the periphery of a mask. In the case of tension masks, if a cheap iron material is used, the masks including its bridge portion expand horizontally, a moire phenomenon occurs on the screen.
To solve the above problems, an objective of the present invention is to provide a tension mask frame assembly of a color cathode-ray tube, by which the transmission of vibration between strips is reduced, the vibration damping effect by the fraction of strips and damper wires is improved, the moire phenomenon due to the interference between electron beams and slots is prevented, and the luminance of pictures is improved.
It is another object to have a tension mask frame that produces a better image quality in a cathode-ray tube.
It is yet another object to have a tension mask that is easy to manufacture and does not increase the cost of manufacture.
To achieve the above objects, the present invention provides a tension mask frame assembly of a color cathode-ray tube, according to a first embodiment of the present invention, the assembly includes a tension mask including a plurality of parallel strips spaced at predetermined intervals apart from each other and a plurality of real bridges for connecting adjacent strips to each other to form slots through which electron beams pass, the number of real bridges gradually decreasing in a direction from the center portion of the mask to the peripheral portion thereof; a frame for supporting the tension mask so that a tensile force is applied to the tension mask in the direction of strips; and at least one damper which is installed on the frame and contact the strips of the tension mask.
In this embodiment of the present invention, the damper is made up of at least one damping Idea wire having both ends secured to the frame, the damping wire contacting each of the strips. Also, the damper can be made up of two damping wires, one end of which is secured to the mask and the other end is secured to the frame.
To further achieve the above objects, the present invention provides a tension mask frame assembly of a color cathode-ray tube, according to a second embodiment of the present invention, the assembly includes a mixed-type tension mask including a plurality of parallel strips spaced at predetermined intervals apart from each other, a real bridge region having real bridges for connecting adjacent strips to each other to form slots through which electron beams pass, the real bridge region being located at the center of the mask, and a dummy bridge region having a plurality of dummy bridges that extend from at least one strip of adjacent strips so that the extending strip does not mechanically contact the facing strip, the dummy bridge regions being located on the peripheral portion of the mask; a frame for supporting the tension mask so that a tensile force is applied to the tension mask; and at least one damper which is installed on the frame and contact the strips of the tension mask.
To further achieve the above objectives, the present invention provides a tension mask frame assembly of a color cathode-ray tube, according to a third embodiment of the present invention, the assembly including a tension mask of mixed type including a plurality of parallel strips spaced at predetermined intervals apart from each other, a real bridge region having real bridges for connecting adjacent strips to each other to form slots through which electron beams pass, the real bridge region being located at the center of the mask, a dummy bridge region having a plurality of dummy bridges that extend from at least one strip of adjacent parallel strips so that the extending strip does not mechanically contact the facing strip, the dummy bridge region being located at the outer side of the real bridge region, and an aperture grille region having a single slot defined by strips, the aperture grille region being located at the outer side of the dummy bridge region; a frame for supporting the tension mask so that a tensile force is applied to the tension mask; and at least one damper which is installed on the frame and contact the strips of the tension mask.